The communication performance of a radio system in conformity with the IEEE802.11 standard significantly deteriorates due to a radio interference fault. Therefore, it is necessary to, when a fault occurs, detect the fault and take measures as soon as possible to stably maintain high reliability of the radio system.
In recent radio systems, a method of detecting a radio interference on the basis of a demodulation error rate of transmission frames (“Intermittent Connectivity Issues in Wireless Bridges”, Cisco Troubleshooting Technical notes, Document ID: 66090, January 2008). This is a method which utilizes a phenomenon that, as for a transmission frame influenced by a radio interference, demodulation processing of the frame fails at a radio station, and demodulation errors, such as a PLCP error and a CRC error, increase. There is also a method of identifying a fault of a radio link between radio terminals (JP-A 2009-117954 (Kokai)).
There are various kinds of causes of a radio interference fault, such as interference between frames due to failure in synchronization between radio stations, interference with a jamming wave of a microwave oven, Bluetooth™ or the like using the same frequency band, and multi-path phasing due to a reflected wave from a wall or the like. In order to prevent a radio interference fault, it is necessary to take suitable measures according to the causes described above. For that purpose, a technique for accurately identifying even the classification of the cause of interference is required in addition to the conventional interference detection techniques.
Demodulation errors used by the conventional technique are not a phenomenon that occurs only due to a radio interference. For example, a demodulation error also occurs when a radio wave is received at a low reception level due to a long distance or an obstacle. Therefore, the conventional technique has a possibility of presenting a radio interference fault as an erroneous detection result because, though an interference has not actually occurred, demodulation errors increase due to a different fault.